The explosive power of an engine, for example, is generated in sequence in cylinders, but there may be irregularities in the force transmitted to the crankshaft used as the output shaft of the engine. The irregularities appear as torque fluctuations or fluctuations in the rotational speed of the crankshaft. It is known that if a heavy object known as a flywheel is attached to the crankshaft, these irregularities can be corrected with the moment of inertia of the heavy object.
Fluctuations in the rotational speed or torque (hereinafter referred to as fluctuations in rotational speed) of the crankshaft are particularly severe when the crankshaft is rotating at a low speed, such as is the case during idling (hereinafter referred to as low-speed rotation). Installing a flywheel apparatus therefore yields significant advantages.
On the other hand, when the crankshaft is rotating at high speeds, the advantages of installing a flywheel apparatus are small because fluctuations in the rotational speed and the like are small. The effects of correcting fluctuations are greater with greater moments of inertia in the heavy object, but at the same time, more rotational energy is consumed. Therefore, when the crankshaft is rotating at high speeds, the presence of a flywheel apparatus has an adverse effect on fuel efficiency and results in a slower response during acceleration.
In view of this, a need exists for a variable flywheel in which the moment of inertia is large during low-speed rotation and small during high-speed rotation. A variable flywheel is proposed in Japanese Utility Mode Laid-Open Publication No. 56-173241, Japanese Patent Laid-Open Publication No. 5-263874, and Japanese Patent Laid-Open Publication No. 2004-263766.
The variable flywheel disclosed in Japanese Patent Laid-Open Publication No. 2004-263766 will be described with reference to FIG. 8 hereof.
As shown in FIG. 8, a first flywheel 102 is fixed with bolts 103, 103 to one end of a crankshaft 101, a second flywheel 105 is mounted so as to be able to idle on the first flywheel 102 by means of a bearing 104, and a sun roller 106 is integrally formed on the second flywheel 105. Planet rollers 108, 108 are rotatably mounted on support shafts 107, 107 extending from the first flywheel 102. A flywheel having this configuration is known as a flywheel with a planetary mechanism, because the planet rollers 108, 108 revolve around the sun roller 106.
Furthermore, a ring member 109 encircles the planet rollers 108, 108. This ring member 109 can be braked with a brake mechanism 112 provided to a housing 111.
When the brake mechanism 112 is not braking, the ring member 109 idles, and the planetary mechanism therefore exhibits a decelerating effect from the first flywheel 102 towards the second flywheel 105. Therefore, the second flywheel 105 rotates at a low speed when the first flywheel 102 is rotating. As a result, the second flywheel 105 does not exhibit the effects of a flywheel. Specifically, only the first flywheel 102 exhibits the effects of a flywheel.
Fuel efficiency can be improved because the energy for rotating the second flywheel 105 is extremely small. This aspect can be used during high-speed rotation and other such times when rotation fluctuations are small.
When the brake mechanism 112 is braking, the ring member 109 is halted, and the planetary mechanism therefore exhibits an accelerating effect from the first flywheel 102 towards the second flywheel 105. Therefore, the second flywheel 105 rotates at a high speed when the first flywheel 102 is rotating. As a result, the second flywheel 105 exhibits a significant flywheel effect. Specifically, it is possible to achieve a significant flywheel effect with the first flywheel 102 and the second flywheel 105. This aspect can be used during idling and other such times when rotation fluctuations are large.
However, the flywheel with a planetary mechanism shown in FIG. 8 has the following problems.
First, one problem is that the moment of inertia has a narrow variability range. Generally, a greater variability range in the moment of inertia allows for greater variability control. It is advantageous to bring the mass (the flywheel mass, a weight) near the rotational center in order to bring down the lower limit of the moment of inertia. However, in the flywheel with a planetary mechanism shown in FIG. 8, the rotational center is in the crankshaft 101, and the mass therefore cannot be brought near the rotational center. Accordingly, the variability range of the moment of inertia is limited, and variability control is reduced.
Another problem is that two flywheels, namely, the first flywheel 102 and the second flywheel 105, are needed, and the entire weight of the variable flywheel increases, reducing the acceleration/deceleration characteristics (acceleration properties and deceleration properties) of the vehicle. The cost of the flywheel apparatus is also high, and fuel consumption increases.
Furthermore, only two aspects are possible with the application and release of braking with the brake mechanism 112. A larger selection of aspects must be available to more precisely correspond to a very low speed, low speed, medium speed, high speed, and very high speed, for example.